Fix #846; check whether a const or method is set

During the setting of a package will all child elements also be set;
sometimes one of those children is not a descriptor (addressed in #840)
and must the setting be skipped in this case.
Change default template to responsive-twig
Added last two entries
Merge pull request #847 from mvriel/846

[WIP] Fix #846; check whether a const or method is set
Merge pull request #848 from mvriel/846

Fix #846; check whether a const or method is set
Release fixes
Set version number for next release
Merge branch 'release-2.0' into develop
Merge branch 'develop' of github.com:phpDocumentor/phpDocumentor2 into develop
Fix 850: Use new templates and fix issue in writer
Merge pull request #855 from mvriel/850

Fix #850: Use new templates and fix issue in writer
Merge branch 'release-2.0' into develop